According to the Authors of Your Text, Why Did Behaviorists

According to the authors of your text, why did behaviorists not incorporate cognition, thinking, and feeling into their theory?

A) There was no empirical support that these concepts mattered.
B) They used strictly animal models for most of their theories.
C) They consider the concepts too vague and difficult to observe.
D) The theory could become too complex to study empirically.